Autonomous vehicles are increasingly being used in both the underwater and terrestrial (e.g., out-of-water or above-water, on land, aerial, etc.) domains to fulfil tasks previously conducted using manned platforms. No matter the domain, the ability to navigate precisely is a key performance parameter of all autonomous systems.
Underwater autonomy has applications in both commercial and military contexts. For example, underwater scientific research can use underwater vehicles to navigate areas of the ocean floor for a variety of reasons. Unmanned undersea or underwater vehicles (UUVs) are also commonly used in mine warfare to inspect and/or identify mines or other underwater items. Still other example applications for UUVs exist that are not mentioned here. The advantages of UUV technology are multiple, and include economic benefits and the ability to operate in hostile environments without putting personnel at risk.
Many existing autonomous underwater systems utilize inertial navigation systems, combining accelerometer and rate gyroscope measurements with observations of velocity from an acoustic sensor to produce a navigation solution. Such systems require periodic geographic fix data to reduce the effects of the position drift encountered when noisy sensor data is integrated for long periods of time.
Geographic fixes can be provided by surfacing (to acquire a fix from a GPS satellite network), by identification of some known point on the seabed, or from an acoustic tracking system. Returning to the surface for a GPS fix may not be convenient or desirable if the vehicle is operating in deep or hostile water. Furthermore, fixed land marks may not exist in the area being surveyed, and the requirement to track and follow an undersea vehicle is not consistent with many operational autonomous models.
Reference will now be made to the exemplary examples illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.